A principal purpose of a hair cleansing agent resides in removing dirt on hair and scalp, preventing dandruff and itchiness of the scalp, and keeping the hair and scalp clean. In view of obtaining a hair cleansing agent having high cleansing performance, it is preferable to use, as a main cleansing component, an anionic surfactant electrically charged at the equivalent level with the hair and scalp. It is more preferable to use a strong-acid-based anionic surfactant having a sulfuric acid group or sulfonic acid group in the anionic portion thereof, in view of preventing re-adsorption of dirt. Among others, an alkyl sulfate and alkyl ether sulfate are most generally used as the main component of a hair cleansing agent, by virtue of their rich foaming property and excellent cleansing performance.
The alkyl sulfate and alkyl ether sulfate, however, still have problems in terms of mildness to the scalp. Horny layer cells which form 10 to 20 layers in the surficial portion of the skin have important roles of keeping moisture within the skin, and protection from an external stimulation. The above-described alkyl sulfate and alkyl ether sulfate, however, permeate into the horny layer, strongly swell the cells, and elutes natural moisturizing components, such as an amino acid or lipid inherent to the cells, out from the cells. Accordingly, repetitive use of such hair cleansing agent, containing these surfactants as the main component, may tend to dry the skin due to the lowered moisture content of the scalp, and tend to induce itchiness of the scalp or provide a larger amount of dandruff because the surfactant and some stimulating substance may more readily permeate into the skin.
As low-stimulus cleansing bases, Patent Document 1 proposes an amino-acid-based surfactant such as an anionic surfactant in the form of alkyloylalkyl taurine salt, and Patent Document 2 proposes a weakly-acidic anionic surfactant such as polyoxyethylene alkyl ether carboxylate. The amino-acid-based surfactant and the polyoxyethylene alkyl ether carboxylate are less likely to swell the horny layer, and are mild to the skin. They, however, still have room for improvement as for basic performance of the cleansing agent, such as foamability and cleansing performance.
Patent Document 3 describes a technique of adding conditioning performance to a hair treatment composition. The document describes that a composition excellent in the conditioning performance may be obtained, without degrading the basic performances of the hair conditioner such as foamability and viscosity, by using a specific polyxoyalkylene alkenyl ether acetate.